Proximity sensor minimises mobile device RF exposure

12th November 2015

Nat Bowers

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Datasheet

Expanding its SX9300 family of proximity sensors, Semtech has announced the SX9306, a new addition that minimises RF exposure by selectively reducing RF power in mobile phones and tablets. The SX9306 is an ultra-low power, capacitive proximity sensor with an on-chip smart engine for human body detection and advanced Specific Absorption Rate (SAR) control.

SAR is the measure of the amount of RF power that is radiated into the human body when in a close proximity to a mobile device. In the U.S., SAR standards are set by the Federal Communications Commission (FCC) and these limits are often followed by other countries around the world. In Europe, the standard is set by CENELEC. In China, the standard is set by TENAA.

The on-chip smart engine can detect the permittivity of different surfaces, giving it the ability to accurately discriminate between inanimate objects or human body.

Smartphone manufacturers use this capability to programme their devices to reduce RF emission power when a device is near a human body part. With higher RF-power devices and more extensive device usage, the SX9306 allows these manufacturers to proactively reduce SAR without affecting RF strength during normal usage.

The SX9306 has four high-resolution capacitive sensor inputs with sensing resolution of 0.08fF. Each sensor also features a capacitance-offset compensation of up to 30pF. With its integrated RF shield, the device provides very robust noise immunity and eliminates false triggers that commonly occur in these applications.

David Wong, Product Line Director, Consumer Sensing Product Groups, Semtech, said: “The pervasiveness of smart devices and their usage has triggered an incredible revolution in the habit of human population world-wide. All manufacturers are looking at ways to reduce SAR without impacting the consumer’s experience, which makes proximity sensors an ideal alternative. The SX9306 is our new flagship SAR proximity sensor because it offers the resolution and power draw required to seamlessly control RF performance without the user being disconnected or experiencing a weak signal.”

The SX9306 is available in two space-saving packages: a 3x3mm thin QFN package; or a 1.63x1.23mm WLCSP. The SX9306 is available immediately in production quantities and is priced at $0.81 each for WLCSP (order code: SX9306ICSTRT) and $0.72 each for QFN (order code: SX9306IULTRT) in 1,000 unit quantities.